There are thousands of strains of algae, both naturally occurring and genetically modified, known to exist. A significant portion of these strains are known to produce various organic materials which can in turn have commercial utility, such as but not limited to biodiesel, pharmaceutical and nutriceutical applications. The materials produced by algae are sometimes formed within the cellular walls of the algae, but alternatively they may be excreted and available on the outside surface of the algae. In either case, to isolate the materials, it is usually necessary to first separate the algae from the medium in which they grow, which is typically water based. The concentrated algae, also known as an algae paste or cake, may be able to be processed containing amounts of residual water. Or, it may be preferred, or even necessary, to completely dry the algae prior to further processing.
A number of processes have been developed in conjunction with removing or separating algae at various levels of maturity from the growth medium, again typically water based. The processes have included flocculation, sedimentation, flotation, centrifugation, vibratory separation, micro-screening, filter press methods, belt press methods, and methods involving use of a dry bed. Occasionally, more than one method is used in combination. Generally, the above processes can require substantial energy input to effect separation, and the resultant product will still require further drying before processing to isolate the desired organic material can begin.
In addition, practicing several of the above processes can create indirect disadvantages in the overall process of extracting organic material from algae. For example, flocculation, sedimentation, and flotation methods generally require a batch strategy for harvesting algae which requires removing most of the algae from the growth pond or vessel. This step results in substantially less algae in the pond or vessel to carry on the propagation process which negatively affects productivity. Alternatives to the batch strategy exist, such as the use of multiple tanks to create a semi-batch process. But, this alternative also requires more space, capital and time. Also, several of the above processes can damage or destroy individual algae cells resulting from the stresses imposed by the separation process.